The earthquake took place along the boundary between the
Nazca and
South American tectonic plates at a location where they
converge at a rate of a year. This earthquake was characterized by a
thrust-faulting focal mechanism, caused by the
subduction of the Nazca plate beneath the South American Tectonic Plates. Chile has been at a convergent plate boundary that generates
megathrust earthquakes since the
Paleozoic era (500 million years ago). In historical times the Chilean coast has suffered many megathrust earthquakes along this plate boundary, including the strongest earthquake ever measured, the
1960 Valdivia earthquake. More recently, the boundary ruptured during the
2007 Tocopilla earthquake in northern Chile. The segment of the fault zone which ruptured in this earthquake was estimated to be over long with a displacement of almost 10 meters, or 120 years of accumulated plate movement. It lay immediately north of the segment which ruptured in the great earthquake of 1960. Preliminary measurements show that the entire South American plate moved abruptly westward during the quake. A research collaborative of Ohio State and other institutions have found, using
GPS, that the earthquake shifted Santiago to the west-southwest and moved Concepción at least to the west. The earthquake also shifted other parts of South America from the
Falkland Islands to
Fortaleza, Brazil. For example, it moved Argentina's capital of Buenos Aires about to the west. Several cities south of Cobquecura were also raised by up to 3 meters. The maximum recorded
peak ground acceleration was at Concepcion, with a value of 0.65
g (6.38 m/s2). The locality of
Tirúa south of Concepción recorded a uplift relative to sea level as a result of the earthquake. This is the highest known uplift of the coast resulting from the earthquake. This uplift made a large islet emerge at the mouth of
Lebu River. It is tied with the
1906 Ecuador–Colombia and
2025 Kamchatka earthquakes as the
sixth strongest earthquake ever measured, approximately 500 times more powerful than the 7.0
Mw earthquake in Haiti one month prior
in January 2010.
Aftershocks An
aftershock of 6.2 was recorded 20 minutes after the initial quake. Two more aftershocks of magnitudes 5.4 and 5.6 followed within an hour of the initial quake. Shortly after the mainshock seismologists installed a dense network of seismometers along the whole rupture area. This network captured 20,000 aftershocks in the 6 months after the mainshock and shows a detailed picture of the structure of the Chilean margin. Seismicity is focused in the depth range of and in a deeper band of between depth. Around 10,000 aftershocks occurred in the region of two large aftershocks in the
Pichilemu region. A 6.9-magnitude offshore earthquake struck approximately 300 kilometers southwest of, and less than 90 minutes after, the initial shock; however, it is not clear if that quake was related to the main shock. A separate
earthquake of magnitude 6.3 occurred in
Salta, Argentina, at 15:45
UTC on 27 February, at a depth of ; two people were injured and one died in Salta. This earthquake was followed on 1 March at 06:32
UTC by a magnitude 4.9 aftershock. Four other earthquakes above M5.0, some possible aftershocks, also occurred near the border in Argentina following the Chile earthquake; a magnitude 5.0 earthquake occurred in
Mendoza on 28 February, a M5.3 earthquake in
Neuquen and a M5.2 in
San Juan on 2 March, and a M5.1 quake in Mendoza on 4 March. Another strong earthquake occurred on 4 March, at 22:39 UTC in
Antofagasta in northern Chile, with a magnitude of 6.3. Minor quakes generated by the main one could be felt as far away as
São Paulo, Brazil, located about away from
Concepción. Since the major earthquake, and as of 15 March, at least four to forty >M5.0 earthquakes have been recorded daily in the vicinity of the main earthquake, including four above magnitude 6.0 between 3 and 6 March. On 11 March, the
March 2010 Chile earthquake (magnitude 6.9, treated by some as an aftershock of the February 2010 earthquake) was reported, followed quickly by further aftershocks measuring 6.7 and 6.0. The epicenter of the 6.9 quake was in
Pichilemu,
O'Higgins Region. On 15 March, two aftershocks of the February 2010 earthquake were reported, one at magnitude 6.2 at 08:08:28 local time offshore
Maule, and another at magnitude 6.7 with the epicenter located offshore the Biobío Region, near
Cobquecura, at 23:21:58 local time. This tremor was followed by two minor aftershocks, one occurring 45 minutes later, measuring M5.5. No tsunami was reported and there were no tsunami warnings issued. On 17 March, at 14:38:37 local time, an earthquake of magnitude 5.2 was recorded in
Aisén, in Southern Chile. Another magnitude 5.2 earthquake was recorded in
Los Lagos the next day. On 26 March, at 10:52:06 local time, a magnitude 6.2 earthquake hit the
Atacama region, in Northern Chile. The
Biobio Region of Chile had strong aftershocks of this earthquake. The first one was a magnitude 6.7
MW earthquake that struck off the coast of
Biobío,
Chile, at 23:21 on 15 March 2010 at the
epicenter, at a depth of . The second earthquake struck on land in the region at 22:58 (
UTC) on 2 April 2010 at 5.9
MW and at a depth of . The third struck on 10:03 (
UTC) on 23 April 2010 at 6.2
MW. The
Pacific Tsunami Warning Center said that historical data indicates that this quake would not generate a tsunami but still advised of the possibility. On 3 May, at 19:09 a magnitude 6.4
MW earthquake struck off
Biobío,
Chile, at the
epicenter, at a depth of . The epicenter was south of
Lebu. On 14 July 2010, another 6.5 magnitude earthquake occurred in the area.
2011 aftershocks On 2 January at 17:20:18 local time, a 7.1 magnitude aftershock occurred northwest of
Temuco, Chile. On
Lautaro,
Cañete,
Nueva Imperial,
Traiguén and
Carahue the quake was felt at intensity VI (
Strong) of the
Mercalli intensity scale. In Temuco it was perceived at intensity V (
Moderate). In
Talcahuano,
Concepción,
Chillán,
Osorno and
Valdivia it shook at intensity IV (
Light). According to the
USGS the earthquake's epicenter was located on the ground, east of the coastal town of
Tirúa in the
Araucanía Region. However, according to the
University of Chile's Seismological Service, the seismic event was located off the coast of Tirúa, measuring a magnitude 6.9
ML. The University of Chile also reported that the localities that received the strongest shaking (VI) were
Curanilahue,
Lebu and
Tirúa. In Concepción, Talcahuano and Temuco it was felt at intensity V, and in Chillán and Valdivia at intensity IV. A magnitude 6.2 Mw aftershock struck the coast of
Biobío,
Chile at a shallow
depth of on 1 June 2011 at 08:55 local time (12:55
UTC). It was centered just offshore
Arauco Province near a moderately populated area, with most structures in its vicinity reported to be resistant to earthquake shaking. Strong shaking registering at VI on the
Mercalli intensity scale was felt in
Lebu, just south of the epicenter, lasting for approximately one minute. Some residents in coastal areas panicked and evacuated their homes. The earthquake was followed by a moderate magnitude 5.1 Mw tremor that occurred about 52 minutes later to the northeast of the main shock epicenter at an estimated depth of . Initial estimates from the
USGS placed its intensity at a magnitude of 6.4 Mw.
Geophysical impact Seismologists estimate that the earthquake was so powerful that it may have shortened the length of the day by 1.26
microseconds and moved the Earth's figure axis by 2.7 milliarcseconds (about 8 cm). Precise
GPS measurement indicated the telluric movement moved the entire city of Concepción to the west. The capital
Santiago experienced a displacement of almost west, and even
Buenos Aires, about from Concepción, shifted . It is estimated that Chile's territory could have expanded as a result. The earthquake also caused
seiches to occur in
Lake Pontchartrain to the north of
New Orleans, United States, located nearly from the epicenter of the quake. In
Antarctica a series of
icequakes were triggered by the 2010 earthquake in Chile. == Damage and casualties ==